Scientists: Farm Chemicals Causing Massive Bee, Bat Deaths

Some neonicotinoids seem to make naturally occurring pathogens much more potent.

July 22, 2013

Insecticidal seed coatings are likely behind the crash in multiple species, some scientists say.

A class of insecticides called neonicotinioids appears to be decimating wildlife, including bees, bats, and amphibians, according to a new multinational study from researchers from the UK, Australia, and the Netherlands.


The research, published in the Journal of Environmental Immunology and Toxicology, reviews existing literature and highlights how increased use of neonicotinoid bug killers since 1991 has paralleled colony (CCD) disorder in honeybees and plummeting populations of wildlife in areas that feature heavy chemical farming. The authors also weave their own hypotheses into the paper, raising more issues that implicate neonicotinoid pesticides in wildlife collapse. The concept is that the nerve-agent chemicals are damaging critters' immune systems, making it harder for them to fight off fungal, parasitic, viral, and bacterial infections, while also wiping out non-target bugs that serve as food for wildlife.

Introduced by Bayer CropScience in the early '90s, the first neonicotinoid, imidacloprid, has a long track record of killing pollinators. According to the study, in 2001, researchers found that small, chronic doses killed bees within just 10 days. Further research found imidacloprid and fellow neonicitinoid fipronil also caused sublethal effects, disrupting bees' ability to forage. That makes sense, since neonicotinoids are designed to disrupt the central nervous system.

The newer class of chemicals was first believed to be safe and is routinely used on fruit, vegetables, and grain crops. The chemicals are also used to coat genetically engineered corn seed kernels. Because neonicotinoids are systemic, the chemicals in the coating travel from the outside of the seed and into the stem and leaves of the plant, and then eventually into the pollen, where bees find it and carry them back to their hives.

Some blame colony collapse disorder on mites, but the authors of this study note that despite treatment for the mites, honeybee populations continue to crash in the United States. Just this past winter, beekeepers lost about half of their hives, unprecedented numbers that actually allow some beekeepers to apply for disaster relief funding.

Some research—and even some pesticide pamphlet information—suggests neonicotinoids like imidacloprid have the ability to make pathogens that occur naturally in the soil thousands of times more deadly to certain organisms.

It's not just honeybees that are being wiped out. Reports of massive wild bumblebees die-offs in the U.S. and Canada started trickling in during the late '90s. The authors point to research showing that of the 14 species that had been abundant in the same areas in the early 1970s, "three had disappeared completely and five of the remaining 11 were in steep decline," the authors of the study wrote. "In 2008, the Xerces Society for Invertebrate Conservation reported that "at least four species of formerly common North American wild species have experienced catastrophic declines over the past decade—two of them may be on the brink of extinction"

Studies published in 2010 and 2012 found that sublethal imidacloprid levels detectable in normal field conditions stunted bee growth and led to an 85 percent reduction in new queens.

Amphibians & Bats
There's more research to be done to prove a definitive link between neonicotinoids and amphibians, but the researchers note that some chemicals in this class remain stable and potent for months or even for more than a year, even in water. The study authors wrote: "Our hypothesis is, as had been proved with honeybees, that exposure to small doses of the three neonicotinoid insecticides is likely to have occurred and may have weakened the amphibian immune systems, such that they became more susceptible to pathogens."

They say the same is true for bats. As neonicotinoid use really ramped up in the early and mid-2000s, white nose syndrome (WNS), an easily spreading fungal virus, started decimating hibernating bat populations. In 2012, the U.S. Fish & Wildlife Service estimated up to 6.7 million bats died due to the new pathogen. That's a blow to the food system, too, since bats are free forms of pollination and organic insect control.

The study authors wrote: "Imidacloprid, thiamethoxam, clothianidin, and other neonicotinoids applied to the seed on arable crops are nonselective and are toxic to non-target and beneficial insects, as well. Bats are insectivorous species, so their survival has been compromised, since the numbers of insects have been drastically reduced. Again, our hypothesis is that the thousands of invertebrates consumed in their diet will inevitably have exposed bats to small cumulative doses of these toxins. In fact, the abnormal neurological behaviour, which is also pathognomonic of bats affected by WNS, is very similar to the disorientation described in CCD honeybees that causes delay in foraging or eventual abandonment of the hive.

If you'd like to see neonicotinoids temporarily taken off the market to see if wildlife rebounds in their absence, urge your federal representative to support the Saving America's Pollinators Act of 2013.

Tags: bees